function changeCode(){
  var node = document.getElementById("captcha_img");
  //修改验证码
  if (node){
    node.src = node.src+'?id='+uuid();
  }
}

function uuid(){
  //获取系统当前的时间
  var d = new Date().getTime();
  //替换uuid里面的x和y
  var uuid = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
    //取余 16进制
    var r = (d + Math.random()*16)%16 | 0;
    //向下去整
    d = Math.floor(d/16);
    //toString 表示编程16进制的数据
    return (c=='x' ? r : (r&0x3|0x8)).toString(16);
  });
  return uuid;
};
